Data communication switches typically have forwarding logic for assisting the packet forwarding process. In a conventional packet forwarding logic, a key including addressing and other information is typically used as an input to retrieve a result including forwarding information as an output.
With the emergence of quality of service (QoS), many switching protocols, such as IEEE 802.1Q and Differential Services (DiffServ), allow modification, or “shaping”, of QoS information in inbound packets as part of packet processing. The modified QoS information is typically determined as a function of inbound QoS information and other flow properties such as the receiving port. The inbound QoS information should therefore be added to the array of information considered in the course of packet processing.
Many packet processing schemes accomplish this by simply adding the inbound QoS information into a packet forwarding logic input key. By integrating the inbound QoS information into the input key, the packet forwarding logic (through the resulting output) provides customized QoS shaping information for each combination of the inbound QoS information, addressing information and other information.
However, such individually tailored QoS shaping information typically comes at the price of a substantial increase in input key complexity. For example, this typically imposes considerable additional memory requirements, and often provides more flexibility than is needed since network administrators typically desire to provide an identical QoS shaping to packets that include many different combinations of flow properties. Moreover, to the extent it is desired to augment conventional packet forwarding logic with QoS shaping characteristics, a technical obstacle may be presented by hard-coded key size limits that are difficult to upgrade.
Accordingly, there is a need for a QoS shaping scheme for a data communication switch that is realizable without integrating the inbound QoS information into the input key.